Telephone system



y 1941- J. w. CLARK .ETAL

TELEPHONE SYSTEM Filed April 25, 1939 2 Sheets-Sheet 1 L. G. SCH/MPF lA/VENTORS: W LARK ATTORNEK J. W. CLARK E AL TELEPHONE SYSTEM Filed April 25, 1939 sue.

FIG. 2

2 Sheets-Sheet 2 L. G. SCH/MPF INVENTORS CLARK ATTORNEK Patented May 20, 1941 TELEPHONE SYSTEM John W. Clark, Urbana, and Luther G. Schimpf, Jackson Hights, Ill., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a, corporation of New York Application April 25, 1939, Serial No. 269,840

9 Claims.

This invention relates to telephone systems and particularly to systems in which automatic switches are used for establishing connections.

The object of the invention is the provision, through an allotter device, of a common source of power for the magnetsof each line-finder selector switch of a group available to a group of calling lines. In particular, it is contemplated that this common source of power shall be a space discharge device which is actuated whenever a line initiates a call and which is adapted to oscillate in a manner that will provide impulse current to each of the magnets of the selectortaken into use.

The principal feature of the invention is, therefore, the provision of a common allotter for a group of finder switches which is provided with a space discharge device adapted to control the operation of the stepping magnets of the switch taken into use by a calling line.

The foregoing and other features of the invention will be described in detail in the following specification, which should be taken in conjunction with the accompanying drawings, in which:

Figs. 1 and 2, when placed side by side, represent, schematically, a telephone system in which the features of the invention are disclosed in connection with automatic switches of the wellknown two-motion step-by-step type.

It isytobe understood, however, that the embodiment of the invention in this particular system is given by way of illustration only andthat the invention may be applied to any common control circuit supplying power through a space discharge device to the magnets of switching devices selectable by said common control circuit.

Referring to the drawings, there are shown a calling subscribers station A and the associated line circuit LC, another subscribers station D, one of a plurality of line-finder switches LF accessible to the station A through the allotter circuit AC, a selector switch S, a connector switch C and a called subscribers station B.

The subscribers stations A, B and D are each provided with the usual subscribers set which is equipped with a dial for controlling the establishment of desired connections. The selector switch S and the connector switch C are of the well-known step-by-stepor Strowger type, and reference may be had to pages 53 to 67, inclusive, of the second edition of Automatic Telephony by Smith and Campbell for a detailed description of the operation of the circuits associatedwith these switches. Only those portions of the cir:

of each of the line-finder switches available to the line groupstypified by lines A and D. Tube -T is of the heater gas-filled type which breaks down and becomes conducting when the potential on its control electrode becomes sufiiciently positive with respect to the cathode potential of the tube. Each individual line circuit of a group, such as line circuit LC, has access to the allotter by way of a common start relay 1, and when a call is originated by a subscriber, it operates to cause the allotter to take into use the line-finder switch with whose terminals the brushes of the switch of allotter circuit AC are then engaged, whereupon the line finder so taken into use operates to engage the terminals of the calling line and to extend said line to the first selector, after which the allotter is operated to preselect another idle line finder in readiness for serving another calling line.

Each line circuitterminates in a set of three terminals appearing in the terminal banks of the line-finder switch, as indicated by the individual line circuit LC which terminates in terminals 2|, 22' and 23'. The line-finder switch LP is of the well-known step-by-step type provided with two banks of one hundred sets of terminals each, such as the set including terminals ll, 22 and 23 and the set including terminals 2|, 22' and 23'. The terminal sets in each bank are arranged in-ten horizontal levels, each level consisting of ten horizontal terminal sets and selectable in the upper bank by brushes El, 52 and 53, and in the lower bank by brushes 6 l 6'2 and 63'.

These brush sets, by means of a common shaft,

(not shown), are advanced vertically to the proper level and then horizontally to the terminals of the calling line under control of the vertical magnet 20 and the rotary magnet 3|, respectively, each of said magnets obtaining their energizing current from the anode circuit of tube T, as will be described hereinafter. The line finderis provided with a vertical commutator 5 having ten conducting segments, one segment for each two corresponding levels of the line-finder bank terminals. Associated with this commutator is a brush 24 which is mounted on the common brush shaft (not shown) and advances simultaneously with brushes 8| to 33', inclusive, during vertical stepping. When the level of the calling line is reached, the brush sets are rotated under the influence of th rotary magnet 3! until brush E2 (or brush 63 depending on the bank in which the line is located) encounters the sleeve terminal of the calling line, after which said calling line is switched through to the first selector in the known manner.

The operation of the above circuits will now be fully set forth in detail in the following description of a call from station A to station B.

When the subscriber A originates a call, a circuit is completed for line relay I extending from battery through its left winding, left contacts of cut-off relay 2, over the line loop, right inner contacts of relay 2, right winding of relay l to ground. Line relay I operates and connects round to conductor 3, which is commoned to each line relay of the lines on the same level in each terminal bank and extends directly to the vertical commutator segment which marks the level. Thus if the line A is located in the sixth terminal level, conductor 3 would be extended to segment 6.

Each of the commoned conductors, intermediate a line group and the corresponding commutator segment, is connected to a resistance as, for instance, conductor 3 to resistance 4. The other ends of all said resistances are commoned to one side of the winding of relay 1 so that, upon the operation of a line: relay or relays pertaining to calling lines in any particular level and the consequent connection of ground to the level conductor, a circuit is completed through 4 the level resistance (as for instance, resistance 4) winding of relay 1 to battery. Relay 1 operates and completes a circuit for relay 8 via 1e No. 4 contacts of relay 9. On operating, relay 8 connects ground to junction 6 intermediate resistances IG and H via its own No. 5 contacts and the No. 3 contacts of relay 9. Now tube T is a gas-filled thermionic device of the hot cathode type, and prior to the connection of ground to junction 6, negative battery l2, feeding serially through resistances H, H! and i3 keeps the grid Id of the tube negatively biased, thereby preventing the tube from operating. With the connection of ground to junction 8, the bias voltage is reduced to zero, which condition causes the tube to flash and establish a conducting path between the cathode l5 and anode It in the known manner. This anodecathode circuit is further completed through the winding of retard coil H, No. 1 back contacts of relay [3, conductor 49, brush l9 and the bank terminal vh'th which it is engaged, interrupter contacts of vertical magnet 20 of the line-finder switch preselected by the switch of the allotter circuit AC, to battery. The magnet operates and causes the line-finder brushes 61-63 and 6 l '63' to take one vertical step to the first level of terminals, brush 24 to advance from the normal segment to the first segment and the vertical off-normal switch V. O. N. to close its two sets of contacts.

When the vertical magnet 26 interrupts its driving circuit by breaking its interrupter contacts, the cathode-anode circuit of tube T is dis rupted'and the tube is momentarily rendered iii! non-conducting thereby. However, since the ground connection to junction 6 persists and, therefore, the bias on grid l4 remains at zero, the tube flashes again almost immediately, reestablishing the cathode-anode circuit and causing the vertical magnet 20 to operate and take another step, thereby causing the terminal brushes to be raised to the second level and the commutator brush 24 to be raised to the second segment of commutator 5. In this manner the line-finder vertical magnet 20 keeps on operating and. causing the brushes to be raised to successive levels until the sixth level is reached, at which time commutator brush 24 engages the sixth segment, whereupon a circuit is completed for relay 25 in the allotter. This circuit may be traced from ground on the left contacts of relay I, conductor 3, segment 6 and brush 24, conductor 5i], allotter switch brush 26 and the terminal engaged thereby, conductor 5|, winding of relay 25 to battery. Relay 25 operates and, through its lower set of contacts and the No. 3 set of contacts of relay l8, connects negative battery through lamp 2'! to junction 28 which is intermediate resistances l0 and I3. The negative voltage thus applied to the grid of the tube biases the tube beyond the cut-off point and causes it to disrupt its cathode-anode conducting path. The vertical magnet 20 now releases and causes the brush shaft to come to rest in the plane of the terminal level containing the calling line.

Relay 25 further closes an obvious circuit for relay it over its top contacts; and. this relay, when it operates, looks over its No. 2 contacts to ground on the No. 4 contacts of relay 8, transfers the tube anode path through its No. 1 front contacts and allotter switch brush 29 to the winding of rotary magnet 3| via its interrupter contacts, and disconnects the negative biasing potential from junction 28 by opening its No. 3 contacts. Since ground is still maintained on junction 6' by the operated condition of relay 8, tube T is immediately rendered conducting and the cathode-anode path is then completed through the winding of rotary magnet 3| as above described, said magnet operating to rotate the brushsets 6l63 and SP-63 over the respective terminal levels to which they were previously raised. Relay 25 is released immediately when brush 24 disengages commutator segment 6. Rotary magnet 31 now takes successive steps with each refiringof the tube subsequent to each interruption of its cathode-anode circuit at the interrupter contacts of the magnet.

When the brush set 6l63' reaches the terminal set of the calling line A, battery through the cut-off relay 2 is extended through the right contacts of relay l, sleeve terminal 23 and brush 63, No. 4 contacts of relay 32, lower winding of relay 33, conductor 52, allotter switch brush 34' and terminal, lower winding of relay 9 to ground. Relays 2, 33 and 9 all operate in series. Relay 2, upon operating, locks over its locking contacts to brush 63' and opens the circuit of line relay l which releases and disconnects ground from conductor 3, causing in turn the release of start relay 1, which, on releasing, opens the circuit of relay 8 causing said relay to release after an interval to perform functions shortly tobe described. Relay 9 locks over its upper winding and No. 1 contacts to ground on the N0 l'contacts of relay 8, opens the ground connection to junotion'fi thereby causing the grid bias negative battery 12 again to be applied to the grid M 2,242,776 which, in. turn, causes the cathode-anode circuit of. the tube T to become extinguishedand the rotary magnet 3| to take no more steps. Relay 9 further completes a circuit for relay 35 which extends from ground through its No. 2 contacts, No. 2 contacts of relay 8, No. 3 contacts of relay 35, upper winding of saidrelay to battery, and further opens the circuit of relay,8 which, being of the slow-to-release type, does not release until relay 35 has operated and then looked over its lower winding and No. 3 contacts, conductor 53, allotter switch brush 36 to ground on the lower set of contacts of the vertical off-normal switch V. O. N.

, Relay 33, in operating, joins conductors 4| and 42 to conductors 38 and 39, respectively, over its No. land No. 5 contacts, respectively. The loop circuit of relay 43 in the first selector switch S is; now completed preparatory to the subscriber A receiving dial tone in the well-known manner as a signal to proceed with dialing. The operation of relay 43 closes an obvious circuit for relay 44. Relay 44, on operating, applies ground to conductor 49, which, over the No. 6 contacts of relay 33, looks said relay and extends locking ground to cut-ofi relay 2 via its No. 4 contacts, brush 63 and the right outer contacts of said cut-off relay.

The subscriber A, upon the operation of relay 44, receives dial tone in the known manner and then proceeds to dial the wanted number in response to which the selector S and connector C are set to extend the connection to the wanted line. Inasmuch as these operations are old and the apparatus and circuits therefor form no part of the present invention, they have been but briefly indicatedherein and schematically shown in the drawings.

The operation of relay 35 causes the opening of its operating circuit at its No. 3 co'ntacts,and further completes an obvious circuit for the allotter stepping magnet which now operates under self-interruptions, stepping the brushes of the allotter switch successively over the terminals of busy line finders, as evidenced by ground on the terminals on the arc of the allotter switch accessible to brush 36 which is applied thereto by the operated V. O. N. contacts of busy line finders. Ground on successive terminals maintains relay locked, but when an idle line finder is engaged, the absence of ground on brush 36 causes said relay to unlock and open the driving circuit of allotter magnet 30 whereby the allotter switch comes to rest on the terminals of the line finder thus preselected. When, thereafter, a call is initiated and relay 1 operates as described, said line finder is taken into use and proceeds to hunt for and engage the calling line in the manner already described.

Should the call originate from a line terminating on any one of the upper set of contacts as, for instance, from line D, all operations will be the same as already described if said line D is on the corresponding level with line A except for the fact that battery from the cut-off relay of line D (not shown) will be applied over brush 63, No. 3 contacts of relay 33, lower winding of relay 32, to brush 34 of the allotter switch as already traced for relay 33, whereupon relay 32 (instead of relay 33) will operate, in which event conductors 38 and 39 will be joined to conductors 45 and 46, respectively, in order to out line D instead of line A through to the first selector.

Should line D terminate in a difierent level than the one which corresponds to the level of line A, then all operations will be the'same as. described except for the fact that the ground from the line relay will be connected to the segment on commutator 5 which marks the level of line D, in which event the switch shaft stops as already described when this level is reached.

When conversation is over and the calling subscriber restores his receiver, relay 43 releases, in turn releasing relay 44 which, in turn, releases relay 33. When said relay has released it completes a circuit path for release magnet 48 extending fromground on the lower contacts of relay 44, upper set of contacts on switch V. O. N., conductor 41, No. 2 contacts of relay 32, No. 2 contacts of relay 33, winding of release magnet 48 to battery, causing said magnet to operate and restore the line-finder brush shaft to normal.

While the invention has been described with respect to a common rotary switching allotter controlling a group of line-finder switches of known construction, it is to be understood that various other applications and embodiments thereof may be made by those skilled in the art without departing from the spirit of the invention as defined within the scope of the appende claims. 7

What is claimed is:

1. In a telephone system, a plurality of lines, a plurality of line-finder switches accessible to said lines, each of said switches being provided with a driving magnet, an allotter circuit for said switches adapted to be connected to an idle one of said switches, and a gas-filled tube in said allotter circuit operatively responsive to one of said lines when calling for operating the magnet in the line-finder switch to which said allotter circuit is connected.

2. In a telephone system, a plurality of lines, a plurality of line-finder switches accessible to said lines, each of said switches being provided with a vertical driving magnet and a horizontal driving magnet, an allotter circuit for said switches, a gas-filled tube in said allotter circuit operatively responsive to one of said lines when calling for operating in succession the vertical magnet and the horizontal magnet in the linefinder switch to which said allotter circuit is connected.

3. The combination with a group of settable switching devices each provided with a magnet for setting the same, of an allotter circuit for said devices comprising means for connecting said allotter circuit to any one of said switching devices, a gas-filled tube, means for completing the anode circuit of said tube serially through the magnet of the switching device connected to said allotter circuit, and means for rendering said tube conducting whereby said magnet is operated to set said switching device.

4. The combination with a group of settable switching devices each provided with a plurality of magnets for setting the same, of an allotter circuit for said devices comprising a gas-filled tube, stepping means for connecting the anode of said tube serially with a magnet of said plurality of magnets of any one of said switches, means for transferring said anode to each one of the remaining magnets of said switch, means for rendering said tube conducting and nonconducting in succession for operating each of said magnets to set the associated switching device, and means responsive to the setting of the switch for operating said stepping means to connect the anode of said tube with a magnet of another switching device.

5. In a telephone system, the combination with a group of switching devices each provided with a magnet means for setting the same on a set of terminals associated with a calling line, of an allotter circuit for said devices comprising a gasfilled tube, stepping means for connecting the anode of said tube serially with the magnet means of any one of said switches, means controlled by said calling line, for rendering said tube conducting whereby the magnet means with which the anode of said tubeis connected is operated to set the associated switching device on the set of terminals of said calling line, means for restoring the tube to its non-conducting state upon the setting of said switch, and means for operating said stepping means for connecting the anode of said tube with the magnet means of another switching device.

6. The combination with a group of plural motion settable switching devices each provided with a magnet for each direction of motion, of an allotter circuit for said devices comprising a gas-filled tube, stepping means for connecting the anode of said tube serially with a magnet of any one of said devices, means for rendering said tube conducting and non-conducting, respectively for operating each of said magnets in succession to set the associated switching device, and means for operating said stepping means for connecting the anode of said tube with the magnet of another switching device.

'7. In a telephone system, the combinatio with a group of lines and a group of line-finder switches adapted for connection with said lines when calling, of an'allotting device for said switches comprising a rotary stepping switch adapted for normal connection with a free linefinder switch, a thermionic device for operating said line-finder switch in response to a call initiatedfrom one of said lines for connecting said switch with said line, and means for operating said rotary stepping switch for connecting the same with another free line-finder switch.

8. In a telephone system, a thermionic device for. supplying power to a plurality of. line-finder;

switches singly and in succession when taken into use in response to calls initiated from a plurality of telephone lines, comprising a normally heated cathode, an anode having a source of potential therefor connected through a driving magnet of one of said switches, a control element normally biased to prevent a space currentfrom flowing between said cathode and said anode, meanscontrolledb-y a line when calling for altermg the biasing potential of said control element to render said tube conducting for operating said magnet,;and means responsive to the connection of the switch associated with said magnet with said calling line for connecting the anode of said tube with a driving magnet of another linefinder switch.

9. A driving circuit for the magnets of a plurality of settable switches comprising a thermionic device having an electron source of emission, an anode path including a source of potential extending through a magnet of one of said switches, a control element for rendering said tube conducting to establish aspace current between said source of electrons and said anode path whereby the magnet in said path is operated, and means efiective upon the settingof the switch for establishing an anode path through a magnet of another of said switches.

JOHN W. CLARK.

LUTHER. G. SCHIMIPF. 

